That is something that can happen with bootcamp, and while it isn't because of a bug or problem with SL, it may because of upgrade to the new OS itself. If you didn't do a clean install with Leopard, and didn't do one with SL, you would easily be more likely to run into an issue like this.
Maybe there are defraggers out there, or something like Onyx or Cocktail would help, but when I encountered this problem with Tiger and the beta Bootcamp (when the problem was more common after reclaiming a BC partition), formatting and reinstalling was the only way to fix it.